The present invention relates to the field of material science and, more particularly, to the field of nanotechnology.
In recent years, a new generation of quantum confined colloidal semiconductor structures has emerged, with more complex shapes than simple quantum dots (e.g., see Alivisatos, A. P. Science 1996, 271, 933-37). These include nanorods (e.g., see Peng, X., et al. Nature 2000, 404, (6773), 59-61) and tetrapods (e.g., see Manna, L., et al. Nat. Mater. 2003, 2, (6), 382-85). Beyond shape, it is also now possible to spatially vary the electron and hole potentials within these nanoparticles by varying the composition. Examples of these new structures include seeded dots, rods, and tetrapods, which contain a CdSe core embedded within a CdS shell (e.g., see Li, J. J., et al. J. Am. Chem. Soc. 2003, 125, (41), 12567-75; Talapin, D. V., et al. Nano Lett. 2007, 7, (10), 2951-59; Carbone, L., et al. Nano Lett. 2007, 7, (10), 2942-50; and Fiore, A., et al. J. Am. Chem. Soc. 2009, 131, 2274-82). These structures may have many uses beyond those envisioned for simple quantum dots, which are frequently employed in luminescent applications (e.g., see Alivisatos, P. Nat. Biotechnol. 2004, 22, (1), 47-52).
A tetrapod nanocrystal has a central core with four arms branching out at tetrahedral angles (see Manna et al.). It has been previously shown that tetrapod arms can be bent. For instance, when a CdTe tetrapod (4 nm wide and 100 nm long arms) is deposited on a substrate through solvent evaporation, the fluid exerts a capillary force which pulls the tetrapod towards the substrate, in some cases permanently deforming the arms (see Cui, Y., et al. Nano Lett. 2004, 4, (6), 1093-98). Salmeron and coworkers used an atomic force microscope to press on the outward-projecting arms of surface-immobilized CdTe tetrapods, and have shown that for forces below 100 nN, the tetrapod flexes elastically (see Fang, L., et al. Chem. Phys. 2007, 127, 184704). Motivated by these observations, Wang and coworkers computationally modeled the electronic level structure of a CdSe tetrapod with different degrees of arm bending, induced by nanonewton forces, and based on their model predicted a red-shift of the energy gap with increasing force applied axially to a vertical arm of a tetrapod with the other three arms either fixed to a horizontal substrate or the arms in sliding contact with the substrate (see Schrier, J.; Lee, B.; Wang, L. W. J. Nanosci. Nanotechnol. 2008, 8, (4), 1994-98).